This investigation is aimed at an analysis of the functional roles of tropomyosin in the structure and organization of microfilament bundles in animal cultured cells. Using our newly developed method for the isolation of microfilaments from "normal" and transformed cultured cells, we have found that: (1) of five forms of tropomyosin found in "normal" rat cell lines, three are major tropomyosins and two are relatively minor tropomyosins; (2) upon transformation, the level of one or both of the major tropomyosins is decreased and the levels of minor tropomyosins are greatly increased; (3) the degree of these changes in tropomyosin patterns correlates well with the extent of morphological transformation; (4) in terms of the structure of microfilaments, those isolated from transformed cells are much shorter in length than those from "normal" cells. These results imply that this differential expression of tropomyosin between "normal" and transformed cells may be involved in the changes in actin cables associated with morphological transformation. We will purify these multiple forms of tropomyosin and examine in vitro physiological properties of microfilaments with different sets of tropomyosin by various biochemical and biophysical methods. In vivo functional roles of tropomyosin will be determined by microinjection of different forms of tropomyosin or monoclonal antibodies into living cells. We will examine in detail the correlation between the changes in tropomyosin patterns and cell morphology using: (1) Rous sarcoma virus temperature-sensitive mutant infected cells; and (2) mitotic cells. Finally, the genomic arrangement of tropomyosin genes will be determined through the molecular cloning of the genes encoding tropomyosin. The long-term goal of these studies is to understand how differential expression of tropomyosin effects cell morphology changes upon oncogenic transformation and how actin cables rearrange in this process.